A small walnut bolt assay was set up indoors to test the efficacy of entomopathogenic fungi.
Walnut twig beetle (Pityophthorus juglandis), a resident of the Southwestern U.S., has been causing problems in the East as early as 2010. Only a handful of eastern states, including Tennessee, Virginia, Pennsylvania, North Carolina, Ohio, and Maryland, have records of the beetle. Just how did these tiny beetles make it all the way from the arid southwest to the lush forests of the east? Scientists are not certain, but firewood is a likely culprit.
A mature black walnut affected by thousand cankers disease. Photo credit Bud Mayfield.
Walnut twig beetle (WTB) is an insect pest on eastern black walnut (Juglans nigra), an incredibly valuable tree found in small pockets through the central and eastern United States. Beetles feed just under the bark on live phloem tissue and, when populations are big enough, they can girdle stems and branches causing trees to die back. To complicate matters, WTB carries a fungal pathogen (Geosmithia morbida) that infects live tissue causing Thousand Cankers Disease.
We harvested fresh, uninfested black walnut from a supremely generous landowner's plantation in NC. The end of those bolts were sealed with wax, so they can remain as fresh and as appealing as possible to any WTB passing by.
This past week we were in Knoxville at the University of Tennessee Center for Renewable Carbon setting up an experiment with collaborators from the USDA Agricultural Research Service, Cornell University, and UT-Knoxville. We are testing the efficacy of several entomopathogens to either kill, maim, or otherwise adversely impact WTBs infesting black walnut. An entomopathogenic fungus acts like a parasite on insects and can penetrate the beetle's exoskeleton. Our goal is to reduce beetle populations in order to limit the formation of galleries thereby reducing the impact of Thousand Cankers Disease. Walnut trees have a better chance of survival if beetle populations can be reduced or eliminated.
Entomologist Michael Griggs with ARS mixing up a batch of entomopathogen spray.
One of our small bolts being treated with entomopathogenic fungi.
Entomologist John Vandenberg with ARS populating small assay bolts with WTB. Photo credit Bud Mayfield
Louela Castrillo from Cornell University populating small assay bolts with WTB. Photo credit Bud Mayfield.
Robert Camp with UT-Knoxville deploying a treated large bolt into one of our infested trees.
One of our treated bolts secured with rope in the canopy of an infested walnut tree. Photo credit Bud Mayfield.
